1. Field of the Invention
The invention relates to an apparatus for etching a wafer while horizontally holding a single wafer and rotating the wafer.
2. Description of Related Art
Generally, a manufacturing process of semiconductor wafers comprises: slicing a wafer from a single crystal ingot; facing and mechanically grinding (lapping) the wafer; etching the wafer; mirror polishing (polishing) the wafer; and cleaning the wafer. Through such steps, wafers having highly flat surfaces are manufactured. During the manufacturing process, a wafer is subjected to various mechanical workings such as cutting a block from the ingot, grinding the outside cylindrical surface of the block, slicing the wafer from the block, and lapping the wafer. As a result, the upper side of the wafer includes a damaged-layer as a work-affected layer. During the manufacturing process of semiconductor devices, the damaged layer of the wafer induces crystal defects such as slip dislocations to occur, and thereby deteriorating the mechanical strength of the wafer and causing adverse effects on the electrical property of the wafer. Therefore the damaged layer needs to be removed completely. In order to remove the damaged layer from the wafer, the wafer is subjected to etching treatment. Currently, immersion etching and etching by a single-wafer process are applied as the etching treatment.
Since the above-described etching by a single-wafer process is capable of controlling the surface roughness of a large-sized wafer, and the texture-size of the wafer, it is regarded as an optimal method for etching a wafer and has been subjected to examination. The etching by a single-wafer process is a method for etching a wafer by dropping an etching fluid on the upper surface of a flattened single wafer, horizontally rotating (spinning) the wafer so as to spread the dropped etching fluid over the whole area of the upper surface of the wafer, and etching the wafer. The etching fluid supplied to the upper surface of the wafer is applied with centrifugal force caused by rotation of the wafer in the horizontal plane, and the etching fluid is spread all over the wafer surface from a portion to which the etching fluid is supplied to the edge of the wafer. Therefore, the upper surface and the edge of the wafer are etched simultaneously. Most of the etching fluid supplied to the wafer is scattered from the wafer by centrifugal force and is recovered in a cup or the like provided in the etching apparatus. However, a certain amount of the etching fluid passes round the wafer edge to the undersurface of the wafer, and etches the edge portion and undersurface of the wafer.
In order to avoid the etching of the edge portion and undersurface of the wafer, Patent Document 1 (Japanese Unexamined Patent Application, First Publication No. H11-289002: see claims 1, 2, paragraphs [0010], [0018], [0019] and [0021]) discloses a single-wafer processing apparatus. In that apparatus, a center axis of a rotation base is connected to a rotation driver; a positioning portion for mounting a wafer on a predetermined position is provided at the peripheral portion of the rotation base; a support member for supporting the circumference of the wafer is disposed between the positioning portions at the periphery of the rotation base; and a treatment nozzle for supplying the etching fluid is disposed at the position above the rotation base. In such a single-wafer processing apparatus, the relative height X of the positioning portion and the support base compared with the undersurface of the wafer making contact with the rotation base is within a range of 0<X<(A+0.5), where A mm is the thickness of the peripheral portion of the wafer. In addition, in the above-described processing apparatus, a block for a gas supply is disposed around the central axis beneath the rotation base, and gas supply unit is disposed penetrating the interior of the rotation base. The gas from the block is supplied through the gas supply unit.
In such configurations of a single-wafer processing apparatus, by controlling the projecting height of the positioning portion and support member so as to satisfy the above-described range of relative height, it is possible to suppress the generation of turbulence and rebound of the etching fluid. In addition, by supplying a gas from the supply unit disposed at the block, it is possible to increase the atmospheric pressure in the space between the rotation base and the undersurface of the wafer, thereby preventing the etching fluid from passing round to the undersurface of the wafer.
In the conventional single-wafer type processing apparatus exemplified by the above-described apparatus of Patent Document 1, by supplying the gas to the space below the wafer, the etching fluid is prevented from passing round to the undersurface of the wafer. However, there is a possibility that the etching fluid stays for a long duration at the peripheral portion of the wafer causing undesirable etching of the edge portion subjected to the staying etching fluid. In such a case, the chamfered shape of the periphery of the wafer is deformed by the etching, and the edge of the wafer is etched heterogeneously.
In addition, in the conventional single-wafer type processing apparatus described in the above-described Patent Document 1, there is a possibility that the gas supplied to the space below the wafer scatters the etching fluid. The scattered etching fluid may be rebound by the inner wall of the apparatus and adhere again to the upper surface of the wafer.
The object of the present invention is to provide an apparatus for etching a wafer by a single-wafer process and a method for etching a wafer by a single-wafer process that prevent etching fluid from passing round towards the undersurface of the wafer as well as preventing re-adhesion of the etching fluid to the upper surface of the wafer and further preventing the localized deformation of the edge portion of the wafer.